Apparatus commonly known in the art as “power tongs” are used to screw together (or “make up”) and unscrew (or “break out”) threaded tubular connections joining sections (frequently called “joints”) of tubulars. Such tubulars are frequently used in the drilling, servicing and completion of oil and gas wells, in the form of drill pipe, tubing, and other similar tubular goods. Such apparatus are commonly referred to as “tong units” or “power tongs,” which use toothed dies carried by tong jaws, to transmit torque to the tubular connection. While power tongs take various forms, typically the tong jaws are rotated by a ring gear, which may be in turn rotated by one or more, typically two, idler gears. The idler gears are rotated by a gear rotated by a power rotary source, typically a hydraulic motor; this gear (the driver gear) is commonly known as a pinion gear. The different gears, taken together, form a gear chain.
Some power tongs are known as “open throat” tongs, which means that the body and ring gear of the tongs have a window or opening which permits a tubular to be moved into and out of the central opening of the ring gear. Other power tongs are of the closed throat configuration, which means that the tubular must be inserted longitudinally into the ring gear opening. Open throat tongs typically have a gear train comprising one or more idler gears. Closed throat tongs may omit the idler gear(s), and drive the ring gear directly by the pinion gear.
It is to be understood that the foregoing description of moving a tubular into and out of the central opening of the power tong is merely one way to describe relative movement between the tubular and the power tong; same could also be described as moving the power tong into and out of position around the tubular.
As can be understood, the tooth elements of the gears of the gear chain wear over time, causing increased vibration and noise in operation of the tong. In known prior art power tongs, remediation of this situation involves replacement of the gears, with the worn gear teeth being re-machined if possible. It can be appreciated that replacement of an entire gear due to tooth wear is expensive, particularly in the case of the ring gear, which is a large, heavy and expensive component.
Open throat tongs, while offering increased convenience and operational efficiency due to the ability to open the tong unit up and place it around the tubular, have the structural drawback of a discontinuous ring gear and tong housing. Under high load (i.e. high torque) conditions, the ring gear and/or housing can open up or spread, resulting in a loss of transmitted torque. Known open throat tong designs have attempted to lock in the removable ring gear section to the balance of the ring gear, with various limitations on same. In addition, known open throat tong designs require one or more personnel to manipulate, by hand, the door on the front of the tong which creates the open throat. This requirement of personnel presents efficiency and safety issues.